Plasma membrane vacuolar H+ATPases (V-ATPases) have an essential role in renal bicarbonate transport, osteoclast bone resorption, and macrophage pH homeostasis. These transporters account for one third of proximal tubule bicarbonate reabsorption, and for the majority of H+ transport in the collecting duct, where fine control of acid secretion occurs. V-ATPases on the ruffled membranes of osteoclasts are crucial for creation of the acidic microenvironments required for bone resorption, and on macrophage plasma membranes are essential for intracellular pH regulation in acidic environments such as abscessed tissue. Vacuolar H+ATPases are present at low densities in the vacuolar system of all eukaryotic cells. In specialized proton-secreting cells such as the proximal tubule cell, intercalated cell, osteoclast and macrophage, vacuolar H+ATPase expression is greatly amplified, and the high enzyme density on the plasma membrane confers the capacity for cellular proton secretion. The goal of this proposal is to identify mechanisms responsible for amplified H+ATPase expression in specific cell types by analyzing the control of the vacuolar H+-ATPase subunit transcription.
The specific aims are: 1a) to isolate and characterize a potentially novel transcription factor that regulates vacuolar H+-ATPase expression in cells of the monocytic lineage; 1b) to determine the tissue distribution and expression patterns of this factor; 2) to define cis- acting elements required for high levels of vacuolar H+-ATPase expression in the proximal tubule of the kidney; and 3) to verify the role of vacuolar H+-ATPase promoter elements through construction of a transgenic mouse model. These studies will aid in understanding the genetic regulatory elements that are required for terminal differentiation of specialized proton- transporting cells. The information obtained may also provide new insights on mechanisms of abnormal osteoclast function in bone disease, macrophage malfunction in immunodeficiency disorders, and the disorders of urinary acidification common in renal disease.
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